Possibility of persistent voltage observation in a system of asymmetric superconducting rings

Abstract

A possibility to observe the persistent voltage in a superconducting ring of different widths of the arms is experimentally investigated. It was earlier found that switching of the arms between superconducting and normal states by ac current induces the dc voltage oscillation in magnetic field with a period corresponding to the flux quantum inside the ring. We use systems with a large number of asymmetric rings connected in series in order to investigate the possibility to observe this quantum phenomenon near the superconducting transition where thermal fluctuations switch ring segments without external influence and the persistent current is much smaller than in the superconducting state.

The Meissner effect puzzle and the quantum force in superconductor

“…This "force" (6) describes only momentum change in a time unity because of the quantization (2) observed at switching of a ring from normal to superconducting state or between superconducting states with different connectivity of the wave function, Fig.1. The angular momentum change ∆M p = (2m/q)I p S of mobile charge carriers is observed at the transition into superconducting state with I p = I p,A 2(n − Φ/Φ 0 ) = 0, for example in [11,14,16]. The angular momentum change of the crystalline lattice of ions did not observed directly for the present.…”

“…Consequently the dissipation force on average in time F dis = Θ −1 Θ 0 dtF dis may be described with the relation l dlF dis /2π = − (n−Φ/Φ 0 )f sw when the ring is switched with a frequency 1/Θ ≪ f sw ≪ 1/τ RL between superconducting and normal states. The experiments [11,14,16] testify to a non-zero average value F dis at Φ = nΦ 0 and Φ = (n + 0.5)Φ 0 because of the predominant probability P n ∝ exp −E n /k B T of the superconducting state with the same number n at (n − 0.5)Φ 0 < Φ < (n + 0.5)Φ 0 .…”

“…For example, it is observed at measurements of the critical current I c [11,14,16] when the external current I ext used for I c measuring switches at I ext = I c the ring in the normal state n s = 0 at each measurement and the ring comes back in superconducting state n s = 0 when the I ext value decreases down to zero, see Fig.2,3 in [14]. The quantum periodicity I c (Φ/Φ 0 ) [11,14] testifies to non-zero persistent current I p,A = 0 in superconducting state whereas in the normal state the electrical current I(t) = I p exp −t/τ RL circulating in a ring with an inductance L should decay during the relaxation time τ RL = L/R because of a non-zero resistance R > 0.…”

“…The quantum periodicity I c (Φ/Φ 0 ) [11,14] testifies to non-zero persistent current I p,A = 0 in superconducting state whereas in the normal state the electrical current I(t) = I p exp −t/τ RL circulating in a ring with an inductance L should decay during the relaxation time τ RL = L/R because of a non-zero resistance R > 0. The time of each measurement of the critical current I c [11,14,16] is much longer than the relaxation time τ RL = L/R. Therefore the current changes from I = 0 to I = I p = I p,A 2(n − Φ/Φ 0 ) at each return of the ring in superconducting state.…”

“…Consider the switching with a frequency f sw ≪ 1/τ RL of the whole ring between superconducting and normal states observed, for example, at the measurements of the critical current I c [11,14,16], see the section 2.3. In the superconducting state the circular electrical current equals I = I p = I p,A 2(n − Φ/Φ 0 ) and the velocity of pairs l dlv = 2πrv = (2π /m)(n − Φ/Φ 0 ) because of the quantization (2,4) whereas in normal state I = 0 and the average velocity v = 0.…”